1. Field of the Invention
The present invention relates to a high-frequency module that transmits and receives a plurality of communication signals by using a common antenna.
2. Description of the Related Art
There have been suggested various types of high-frequency modules that transmit and receive, using a common antenna, a plurality of communication signals utilizing different frequency bands. As an example of such a high-frequency module, the high-frequency module described in Japanese Unexamined Patent Application Publication No. 2008-10995 includes a switch IC, a demultiplexing circuit, and a duplexer.
Here, the demultiplexing circuit is a circuit or circuit element that demultiplexes a plurality of target communication signals, including a transmission signal and a reception signal. Specifically, the demultiplexing circuit is a circuit that demultiplexes a communication signal of GSM (Global System for Mobile Communications) 850 and a communication signal of GSM 900, a communication signal of DCS (Digital Cellular System), and a communication signal of PCS (Personal Communications Services) and a communication signal of a CDMA (Code Division Multiple Access) communication system.
The duplexer is a circuit element that demultiplexes a transmission signal and a reception signal utilizing different frequency bands in a single communication band. For example, the duplexer described in Japanese Unexamined Patent Application Publication No. 2008-10995 is connected to a transmission signal input port, a reception signal output port, and an antenna input/output port (specifically, an antenna input/output port via a switch IC) of a single communication band in the CDMA communication system. The duplexer transmits a transmission signal of the single communication band from the transmission signal input port to the antenna input/output port side, and transmits a reception signal of the single communication band from the antenna input/output port side to the reception signal output port.
As described above, the duplexer demultiplexes a transmission signal and a reception signal in a single communication band. The frequency bands utilized for the transmission signal and the reception signal in the single communication band are relatively close to each other. Thus, duplexers available at present, particularly duplexers that are mounted in high-frequency modules of mobile communication terminals, are constructed by combining a transmission-side SAW (Surface Acoustic Wave) filter whose pass band is a frequency band utilized for a transmission signal, and a reception-side SAW filter whose pass band is a frequency band utilized for a reception signal.
In a duplexer according to the related art, as disclosed in Japanese Unexamined Patent Application Publication No. 2008-10995, a transmission-side SAW filter and a reception-side SAW filter are integrally provided in a single housing.
Thus, in the duplexer according to the related art, a transmission path for a transmission signal (electrode pattern or the like) and a transmission path for a reception signal (electrode pattern or the like) are close to each other. Thus, a high-power transmission signal may leak into the transmission path on the reception signal side, and the isolation between a transmission-side circuit and a reception-side circuit may be degraded.
Also, a further decrease in size may be required for high-frequency modules. The size of each circuit element is an important factor when designing high-frequency modules so as to have a reduced size.